This invention relates generally to voltage regulation circuits, and more particularly, to current controlled voltage regulation circuits using shunt current control components to minimize the change in load current presented to the power supply.
Voltage regulation circuits are required in virtually all electronic applications requiring Direct Current (DC) voltage levels to operate properly. The DC voltage levels are generally derived from an Alternating Current (AC) voltage source, such as a wall mounted AC voltage receptacle or AC voltage generator, and present potentially destructive voltage transients at their respective DC output voltage terminals. Switching mode DC power supplies, as opposed to linear mode power supplies, are often employed to derive the DC supply voltages from the AC voltage power sources, since the higher load currents required of the electronic applications are more readily and efficiently generated using the switching mode power supplies. As a result, transients associated with the fundamental and harmonic components of the switching frequency of the switching mode power supply may contribute to voltage transients on the DC output voltage terminals. Varying load conditions at the DC output voltage terminals are also responsible for voltage transients on the DC output voltage terminals.
The DC supply voltage may also be generated from a DC power source, such as a battery. Battery powered portable laptop computing platforms, for example, generally utilize a switching mode power converter to generate a DC power supply voltage from a DC battery voltage. In general, whether the DC voltage is generated from an AC or DC power source, voltage regulation is required to minimize transient activity at the DC supply voltage terminals.
Varying load conditions at the DC supply voltage terminals significantly contributes to the transient activity. As the load requires more supply current from the DC supply voltage terminals, for example, a dip in the DC supply voltage may be generated due to the inability of the DC-DC converter to react to the increasing current demand. As a result, a voltage dip is generated at the load terminals while the DC-DC converter changes its switching characteristics to accommodate the change in current required by the load. Conversely, as the load requires less current, a corresponding surge in supply voltage is generated at the load terminals, since the DC-DC converter is generating a surplus of current, which causes a surge in the load voltage.
Prior art techniques used to mitigate voltage transients at the load terminals employ increased bulk capacitance values or higher switching frequencies of the DC-DC converters. Increased bulk capacitance levels are effective to provide an increased instantaneous current capability. The larger bulk capacitor can react to increased loading conditions by supplying the instantaneous current required by the load until the DC-DC converter has had time to respond to the transient loading condition. The bulk capacitors, however, are often implemented on a Printed Circuit Board (PCB). The larger bulk capacitors, therefore, require a larger portion of printed circuit board area and become impractical. Increased bandwidth of the DC-DC converter has a practical limit as well, since load transient bandwidth exceeds any practical DC-DC converter bandwidth.
Therefore, it would be desirable to provide a method and apparatus that does not require increased bulk capacitance nor increased DC-DC conversion bandwidth to mitigate voltage transients or ripple. The present invention provides a solution to these and other problems of the prior art, and offers other advantages over prior art voltage regulators. The present invention, for example, allows the designer to reduce the cost of the SMPS, since high-bandwidth operation of the SMPS is obviated through the use of the present invention.
The present invention relates to a method and apparatus for reducing output voltage transients, or ripple, due to time varying load current.
In accordance with one embodiment of the invention, a current controlled voltage regulator includes a control circuit that receives first and second signals indicative of a drive level of the voltage regulator. The control circuit provides a control signal in response to a difference between the first and second signals. A conduction device receives the control signal and decreases conduction if the difference increases and increase conduction if the difference decreases. The change in conduction is substantially proportional to the difference between the first and second signals.
In accordance with more specific embodiments of control circuit according to the invention, the control circuit includes an operational amplifier.
In accordance with another embodiment of the invention, the control circuit includes a first conversion device that receives the first signal and provides a digital representation of the first signal. A second conversion device that receives the second signal and provides a digital representation of the second signal. A third conversion device that receives the first and second digital representations and provides an analog representation of the difference between the first and second digital representations.
In accordance with more specific embodiments of conduction device according to the invention, the conduction device includes a transistor having a first conduction terminal to receive the first signal and a control terminal coupled to receive the control signal.
In accordance with more specific embodiments of the conduction device according to the invention, the transistor includes a field effect transistor.
In accordance with another embodiment of the invention, an article of manufacture comprises a program storage medium readable by a computer. The medium tangibly embodies one or more programs of instructions executable by the computer to perform a method of operating a current controlled voltage regulator. The method comprises receiving first and second signals indicative of a drive level of the voltage regulator, computing a difference between the first and second signals, and controlling a conductive state of a conduction device in response to the difference, wherein the conductive state is changed in proportion to the difference.
In accordance with more specific embodiments of the method to receive first and second signals according to the invention, the method includes using a resistive component to develop a potential difference between the first and second signals, wherein the potential difference is indicative of the drive level.
In accordance with more specific embodiments of the method to compute the difference according to the invention, the method includes receiving the first signal at an input of a first conversion device, receiving the second signal at an input of a second conversion device, and generating the difference at the output of a third conversion device.
In accordance with another embodiment of the invention, a method of operating a current controlled voltage regulator. The method comprises receiving first and second signals indicative of a drive level of the voltage regulator, measuring a difference between the first and second signals, and controlling a conductive state of a conduction device in response to the difference, wherein the conductive state is changed in proportion to the difference.
In accordance with more specific embodiments of the method to receive first and second signals according to the invention, the method includes using a resistive component to develop a potential difference between the first and second signals, wherein the potential difference is indicative of the drive level.
In accordance with more specific embodiments of the method to compute the difference according to the invention, the method includes receiving the first signal at a first input of an amplifier, receiving the second signal at a second input of the amplifier, and generating a substantially proportional difference at the output of the amplifier.
In accordance with another embodiment of the method to compute the difference according to the invention, the method includes receiving the first signal at an input of a first conversion device, receiving the second signal at an input of a second conversion device, and generating a substantially proportional difference at the output of a third conversion device.
In accordance with one embodiment of the invention, in a power supply a voltage regulator controlling output voltage to substantially eliminate voltage variations. The voltage regulator includes a current control circuit that receives first and second signals indicative of a drive level of the voltage regulator. The control circuit provides a control signal in response to a difference between the first and second signals. A current conduction device receives the control signal and increases conduction if the difference decreases and decreases conduction if the difference increases. The change in conduction is substantially proportional to the difference between the first and second signals.
In accordance with more specific embodiments of the current control circuit according to the invention, the current control circuit includes an operational amplifier.
In accordance with another embodiment of the invention, the current control circuit includes a first conversion device that receives the first signal and provides a digital representation of the first signal. A second conversion device that receives the second signal and provides a digital representation of the second signal. A third conversion device that receives the first and second digital representations and provides a signal that is substantially proportional to the difference between the first and second digital representations.
In accordance with more specific embodiments of the current conduction device according to the invention, the current conduction device includes a transistor having a first conduction terminal to receive the first signal and a control terminal coupled to receive the control signal.
In accordance with more specific embodiments of the current conduction device according to the invention, the transistor includes a field effect transistor.
In accordance with one embodiment of the invention, a current controlled voltage regulator includes a control means that receives first and second signals indicative of a drive level of the voltage regulator. The control means provides a control signal in response to a difference between the first and second signals. A conduction means receives the control signal and increases conduction if the difference decreases and decrease conduction if the difference increases. The change in conduction is substantially proportional to the difference between the first and second signals.
In accordance with more specific embodiments of control means according to the invention, the control means includes an operational amplifier.
In accordance with another embodiment of the invention, the control circuit includes a first conversion means that receives the first signal and provides a digital representation of the first signal. A second conversion means that receives the second signal and provides a digital representation of the second signal. A third conversion means that receives the first and second digital representations and provides a signal that is substantially proportional to the difference between the first and second digital representations.
In accordance with more specific embodiments of conduction means according to the invention, the conduction means includes a transistor having a first conduction terminal to receive the first signal and a control terminal coupled to receive the control signal.
In accordance with more specific embodiments of the conduction means according to the invention, the transistor includes a field effect transistor.